Coils are used extensively for the bar antenna, the loop antenna and the pickup coil, as well as for the transformer, the electromagnet, etc. The coils used for these appliances are generally connected thereto with a terminal provided at the end of the lead wire of each coil, or by soldering the extension of the coil thereto.
For some years, on the other hand, transition from "analog" to "digital" is seen in designs of audio sets such as radios, cassette tape recorders with radios, amplifiers and tuners, and of television sets, and an advance is made therewith in making them small in size and in improving the performance thereof. Owing to the enlargement of a pulse waveform resulting from digitization, however, noise increases in each set of the above-mentioned appliances, and thus it turns necessary to keep an antenna apart from the set and connect it to the latter by an extension cord or the like for improving an S/N ratio (signal/noise ratio). In other words, an antenna with an extension cord is necessitated.
A method of manufacturing a bar antenna will be described hereunder for exemplifying a coil usually manufactured. A conventional bar antenna is prepared by inserting a ferrite core 2 through a paper tube 1 as shown in FIG. 6, and a covered copper wire 3 is wound round on the paper tube 1. Moreover, a coil-fixing adhesive 4 is applied thereon so as to prevent a coil thus formed from getting loose. The coil for which the paper tube is used is subjected beforehand to a moisture resistance treatment with wax or the like. Subsequently the end of a cord 5 and the end of a lead wire 6 of the covered copper wire 3 of the coil are twisted together at a connecting portion 7 and soldered, and then they are fixed temporarily with a tape or the like put thereon. In a process just before a case 9 is fitted, an adhesive is applied for fixation.
As described above, the conventional method has faults that it requires much labor and time because of a large number of manufacturing processes it needs, and that breakage of the connecting portion 7, loosening of the coil or the like occurs when strong pulling of the cord 5 or any other similar matter takes place, which results in the lowering of a yield of manufacture.
Moreover, with respect to the structure, it is necessary to prepare an extension cord 5 by soldering a covered cord with the lead wire 6 for employing the antenna outside the set, since the lead wire 6 may not be extended to the outside of the set. Extension of the lead wire 6 in an exposed state to the outside means to expose outside a bare member which is naturally to be housed in the case 9, and this is disadvantageous in design of a commodity for external appearance, feeling of touch, performance, etc., thereof.